We are studying brain parameters to determine the separate and joint effects of under-nutrition (N negative) and environmental deprivation (E negative) on mouse brain development. In preliminary work we found that all three experimental conditions (N positive E positive, N positive E negative, and N negative E positive) produce measurable positive effects on brain weight, brain protein and brain DNA, measured with respect to N negative E positive. Our data are not yet adequate for assessing the existence of synergism (positive or negative) between the two deprivations. Only the N positive E negative configuration has been completed to scientific certainty. Deficits produced by N negative are found at weaning (23 days) and are not at all rehabilitated by physiological maturation as measured after puberty (after 60 days). "Over-nutrition" produced by raising mice in litters smaller than maximal (8/litter) yields increased brain weight, brain protein, and brain DNA. After puberty the positive increments in brain weight and brain protein disappear, while the brain DNA increment persists. After nailing down the data for the two conditions still in preliminary shape (N positive E positive and N negative E positive), we expect to (1) attempt to localize the various increments, and (2) test the possible functionality of the various increments, especially of the extra DNA found in the animals raised in small litters.